Algal Toxin Breaks Ring Record

In 1998, a red tide algal bloom blanketed parts of the southern coast of New Zealand’s North Island. An algae species, Karenia brevisulcata, in the bloom spewed toxins that killed most fish in Wellington Harbour and caused respiratory problems in more than 500 people nearby. Scientists had previously isolated groups of toxins from this species, but the large size of many of the molecules made structural determination difficult. Masayuki Satake of the University of Tokyo and his colleagues have now determined that one of the toxins, brevisulcenal-F, has 17 contiguous rings, making it the longest polycyclic ether system of any marine algal toxin (J. Am. Chem. Soc., DOI: 10.1021/ja212116q). The chemists isolated brevisulcenal-F by passing algae extracts through several rounds of chromatography, picking the fractions that killed mouse leukemia cells. They then determined the molecule’s structure using two-dimensional NMR to resolve the many overlapping signals. To confirm their NMR data, the researchers used tandem mass spectroscopy. Brevisulcenal-F’s 17 contiguous ether rings surpass the structure of the previous record holder, gymnocin-B, which has 15 fused rings.